History TookALevelInJerkass / AnimeAndManga

** After the TimeSkip, Rossiu, now Simon's advisor as head of the human government, becomes rather morally questionable, from going behind Simon's back to force the humans living underground to come to the surface ([[spoiler:thereby triggering the apocalypse he was trying to prevent]]) to [[spoiler:having Simon arrested and sentenced to death for treason simply to use him as a scapegoat]].

* Guts from ''Manga/{{Berserk}}''. After the horrible events of the Eclipse that all but broke him, he spends two years as a ByronicHero who keeps everyone distant from him and is focused solely on killing as many Apostles as he can as he seeks vengeance against the God Hand and Griffith in particular. It is only after reconnecting with Casca, the only other survivor of the Eclipse, that he begins to grow out of this, but this comes at the cost of harboring a pretty horrific EnemyWithin that he needs a new circle of TrueCompanions just to keep in check.
* Canute in ''Manga/VinlandSaga'' after [[spoiler:ascending to the throne]].
* Suzaku from ''Anime/CodeGeass'' took a ''huge'' one during the timeskip, [[BreakTheCutie for obvious and rather justified reasons]]. He never really gets better, and his pain is very apparent, if expressed in the wrong way.
* In ''Anime/YuGiOhGX'', this happens to Kaiser in a big way when he becomes Hell Kaiser, as you can tell from the name change.
** Judai, while he wasn't exactly a ''Jerkass'', did become rather cold and distant to his former friends in season 4.
* Amy Rose of ''Anime/SonicX'' was initially a kindly bubbly girl with occasional {{Tsundere}} [[BerserkButton mood swings]]. By the final episodes she more consistently acts as an obnoxious and occasionally outright violent StalkerWithACrush to Sonic, to the point half her allies, and even some foes, are outright terrified of her.
* Oh Lordy, Nakai from ''Manga/{{Bakuman}}''. When he's first introduced he was desperate to get a manga serialization despite not succeeding in ten years. Through much perseverance he proves himself to fellow manga artist Aoki and the two do manage to start up a serialization. However, once he gets a taste of success it goes right to his head and he starts acting like an arrogant, womanizing asshole, alienating most of his friends and colleagues, ultimately getting himself canceled and decides to quit manga and go back home. [[spoiler:Recently he's returned to the business, but not only is he working for Nanamine, the first unambiguously "evil" rival in the series, but both his appearance and personality have grown even more slovenly and repulsive during the interim. He appears to have a bit of a lecherous streak toward his fellow female assistants, as he's only interested in helping the good-looking ones. After he gets fired due to leaking Nanamine's spot in the ranking to his online consultants, he drunkenly goes over to Aoki's house, intending to hurt her, and nearly gets himself arrested if not for Hiramaru's intervention. He goes back to being an assistant, but he's still far from the good person he used to be.]]
* Most of the former NERV officers after the TimeSkip in the third ''Anime/RebuildOfEvangelion'', especially Ritsuko. Somewhat justified though since the reason everyone is now so hostile towards Shinji is because [[spoiler: he almost destroyed the world.]]
* ''Anime/PuellaMagiMadokaMagica'': This happened in the backstories of both Kyouko and Homura.
** Kyouko used to be a relatively cheerful and idealistic magical girl who, like Madoka and Sayaka, once worked under Mami's wing as a kouhai. Her wish was for people to listen to her father, an excommunicated minister whose family was starving. Once her father found out, he killed himself, his wife and his other daughter, leaving Kyouko as the SoleSurvivor of the Sakura family. Kyouko survived, but turned into a bitter and cynical girl who's willing to let familiars go free and become witches (which will result in the deaths of innocent people) because the familiars won't give her the Grief Seeds that she needs to keep herself alive.
** It eventually turns out that [[spoiler:in previous timelines]], Homura was a glasses-wearing ShrinkingViolet rather than the cold and aloof loner that she appears as at the start of the series. [[spoiler:She made a wish to be able to redo her meeting with Madoka and, as a result of learning the AwfulTruth about being a magical girl and enduring a GroundhogDayLoop full of frustration and despair, ended up becoming jaded and cynical]].
* Chiba and Maho from ''Manga/WanderingSon'' TookALevelInJerkass between the elementary and middle school chapters, though Saori mellowed down and learned to be more pleasant while Maho became more neutral. Saori went through a sort of TraumaCongaLine in late elementary. She was becoming increasingly jealous of Takatsuki's friendship with Nitori which lead her relationship with everyone to sour. Eventually she became bitter and aggressive. Maho on the other hand was under stress of having her crush fall in love with her little sister, along with said sibling being transgender; though she's always been depicted as a [[BigBrotherBully bully]] to Nitorin, just not as bad in early chapters.
* ''Manga/{{Naruto}}'': Sakura in the fillers. While she started to genuinely warm up towards Naruto, the fillers seem to ignore the poor girl's CharacterDevelopment for the sake of [[PlayedForLaughs humor]]. This got to the point where she started taunting Naruto for his misery in the third movie.
** Let's not forget Sasuke in canon. He did this twice:
*** When Sasuke recovered from [[MindRape Tsukuyomi]], he lashed out at [[NeverMyFault Konoha in general]] for his being weaker than Itachi and [[ItsAllAboutMe Naruto in specific for his success in getting stronger]]. This led to him defecting and almost killing Naruto.
*** When Tobi told Sasuke the AwfulTruth, Sasuke went from sparing the lives of insane prisoners to casually murdering guards doing their jobs, not to mention [[spoiler:almost killing Karin because she was captured by the freaking ''Hokage Candidate'']].
** The aforementioned Tobi, the Masked Man, who is revealed to be [[spoiler:Uchiha Obito, having gave up hope on the world and willing to enact the Moon Eye's Plan to trap the entire shinobi in a world created through the Infinite Tsukuyomi, like it or not]].
** [[NiceGuy Iruka]] ''of all people'' takes one in [[{{Filler}} the sixth Shippuden movie]]. Set after a battle with Akatsuki, some of the Konoha 11's parents are offering to recommend to Tsunade that they get promoted to Jonins for their efforts. Naruto, seeing this, goes to him as he's the closest thing Naruto has to a family and asks if he could do the same. Iruka coldly shoots him down and tells him he won't get special treatment just cause he saved the Village from Pain, not even offering to let him get promoted to Chunin or give him a reason why he can't do that.

* A JustifiedTrope in the case of [[spoiler: Tem Ray]] in ''Anime/MobileSuitGundam''. He was already a borderline MadScientist in the beginning, but the biggest leap into jerkassery happened due to [[spoiler: brain damage from oxygen deprivation, which can really screw up your personality.]]
* Arguably, Medaka of ''Manga/MedakaBox''. Since [[GreaterScopeVillain Ajimu]] has introduced five "''normal''" people to her, Medaka no longer views Zenkichi as someone special to her since he couldn't pass the first trial of a test she gave the normals. Then she actively tries to turn him into her enemy by acting cold and offensive just so she can see value in him again. Kind of sad considering it's a combination of her abnormality and her personality that causes her change like this since she can't understand failure or things from a "weak" perspective. She even goes as far as [[spoiler:using an abnormality that makes her weaker than Zenkichi and goes all out in a fight against him. Since Zenkichi isn't really willing to fight her at this point she mops the floor with him. However the abnormality she used is a "perfected version" of Kumagawa's Bookmaker and isn't meant for fighting, but for allowing the person affected to feel the world from the opponents perspective.]]
* Takanashi from ''Manga/{{Wagnaria}}'' is suddenly a lot gruffer in the second season. {{Justified|Trope}} in that dealing with [[DoubleStandardAbuseFemaleOnMale Inami]] will do that to you. Then inverted in that he becomes super-nice to her with even less explanation.
* Chiaki Yoshino from ''Manga/SekaiichiHatsukoi'' went from [[InnocentlyInsensitive bratty but well meaning]] ManChild to immature {{jerkass}}. This might be justified as he's dating his best friend Hatori who is a {{Yandere}} and given that [[spoiler: he was [[RapeAsDrama brutally raped]] and then suddenly forced the two into a relationship based on [[LivingEmotionalCrutch co-dependency]]]] pretty much made him worse as shown when his relationship with his best friend [[UnluckyChildhoodFriend Yanase]] is strained given that he fails to understand Yanase's feelings and not only turns him down multiple times in the worse way possible but constantly rubs salt on the wound. It gets to the point that Yanase does call him out on his attitude...unfortunately, it means nothing in the next episode where Chiaki pulls a huge {{jerkass}} moment that the fanbase [[NeverLiveItDown won't let him live down]] and generally threw him into TheScrappy territory.
%%How?* Almost all the 3-A girls in the Sports Festival arc of ''Manga/NegimaMagisterNegiMagi''.
* The girls of Hinata House, most notably [[spoiler: Kitsune]] and except [[spoiler: Mutsumi]], during the story set in the Kingdom of Molmol in ''Manga/LoveHina''.
* ''Anime/MobileSuitGundamAGE'', Flit Asuno goes from an idealistic shonen hero to a ruthless dictator who is willing to destroy his enemy [[FantasticRacism "race"]] without listening to anyone even his son and grandson. To say that he has taken a level in jerkass is an understatement. As well as [[BreakTheCutie saying]] [[ILetGwenStacyDie there's a]] [[DespairEventHorizon reason]].
* ''Manga/LinebarrelsOfIron'': The main character so incredibly straight until even the helpful support character hates him.
* This is what happens to anyone who's infected with Eclipse (except [[IdiotHero Touma]])in ''Manga/MagicalRecordLyricalNanohaForce''.

* It's stated evolution changes a Pokémon's personality in [[Anime/PokemonTheSeries the anime]] and this is most noticeable with Charizard. As a Charmander he was overall a nice Pokémon, maybe even one of the [[NiceGuy nicest]] Ash owned in the Original Series, but when he evolved into a Charmeleon he TookALevelInJerkass. He stopped listening to Ash and was more violent, and it didn't get any better when he evolved again. After Ash thawed him out when he was frozen by Poliwrath, he regained his loyalty to Ash, and with gradual character development by his reappearance in Unova he was as kind as he was as a Charmander, with only the obligatory flamethrower greeting remaining.
* This is the defining moment for Gabriel, the protagonist of ''Manga/GabrielDropOut'', who at the very beginning of the first chapter/episode, was a sweet, hardworking, respectable and idealistic angel who wanted nothing less than to spread as much happiness as she could... until she discovers VideoGames a few minutes into the first episode/sometime later in the manga. Next time we see her, she has turned into the rude, lazy, cynical, and apathetic slob she will be for the rest of the series, even going so far as to refer to herself as a ''FallenAngel''.
* Ukyo Kuonji gets hit with this ''badly'' during the manga ([[AdaptationalHeroism but not the anime]]) of ''Manga/RanmaOneHalf''. When introduced, she's portrayed as "the sane one" of Ranma's would-be suitors, preferring non-violence in her efforts to win Ranma's heart -- her first scheme is to try setting Ryoga Hibiki up on a date with Akane, because if they got together, then she can have Ranma by default and everyone's happy. She then winds up becoming as violent and destructive as Shampoo & Kodachi, getting involved with them in KickTheDog moments like: trying to assassinate Nabiki when she is Ranma's fiancee, leveling Ranma's family house, and bombing Ranma & Akane's wedding. She also goes from simply being sharp with money to outright exploiting the already-abused Konatsu when he comes to work for her.

* This trope happens subtly to Nate Adams from ''Anime/YokaiWatch'', compared to the video games. Halfway into the series, he becomes less willing to reason with [[MonsterOfTheWeek the Yo-kai from a particular segment]] and more inclined to summon one of his Yo-kai friends to find the way to circunvent their mischievings caused by inspiriting, or outright give them a beating (Jibanyan being his most used choice is an indication), such as his personal beef with Snottle [[spoiler:without knowing he created him [[note]]as one of his snots when he was younger[[/note]] and he never tries to reason to him]]. Ironically, in the games, fighting Yo-kai is needed to befriend them [[note]]Only a handful of Yo-kai are befriended automatically as the plot progresses, so to build their collection the player must engage Yo-kai in combat, impress them and/or give them their favorite food to earn their friendship (also, some S-rank Yo-kai like Venoct, Kyubi, Arachnus, Toadal Dude and the Super Hero Yo-kai are only available post-game)[[/note]]. The fact that he hates being average [[note]]so much that he allowed a Yo-kai to lick him ''everywhere'' to get prizes[[/note]] and that almost every day of his life is thrown upside-down by Yo-kai themselves has to do with it.
* Takeshi Yoshida in ''Manga/Touch1981'' goes from nice fanboy who sincerely admires Tatsuya to arrogant, victory-obsessed prick.

* This is the defining moment for Gabriel, the protagonist of ''Manga/GabrielDropOut'', who at the very beginning of the first chapter/episode, was a sweet, hardworking, respectable and idealistic angel who wanted nothing less, then to spread as much happiness as she could... until she discovers VideoGames a few minutes into the first episode/sometime later in the manga. Next time we see her, she has turned into the rude, lazy, cynical, and apathetic slob she will be for the rest of the series, even going so far as to refer to herself as a ''FallenAngel''.

* It's stated evolution changes a Pokemon''s personality in [[Anime/PokemonTheSeries the anime]] and this is most noticeable with Charizard. As a Charmander he was overall a nice Pokemon, maybe even one of the [[NiceGuy nicest]] Ash owned in the Original Series, but when he evolved into a Charmeleon he TookALevelInJerkass. He stopped listening to Ash and was more violent, and it didn't get any better when he evolved again. After Ash thawed him out when he was frozen by Poliwrath, he regained his loyalty to Ash, and with gradual character development by his reappearance in Unova he was as kind as he was as a Charmander, with only the obligatory flamethrower greeting remaining.
* This is the defining moment for Gabriel, the protagonist of ''Manga/GabrielDropOut'', who at the very beginning of the first chapter/episode, was a sweet, hardworking, respectable and idealistic angel who wanted nothing less, then to spread as much happiness as she could... until she discovers VideoGames a few minutes into the first episode/cut to sometime later in the manga. Next time we see her, she has turned into the rude, lazy, cynical, and apathetic slob she will be for the rest of the series, even going so far as to refer to herself as a ''FallenAngel''.

* This is the defining moment for Gabriel, the protagonist of ''Manga/GabrielDropOut'', who at the very beginning of the first chapter/episode, was a sweet, hardworking, respectable and idealistic angel who wanted nothing less, then to spread as much happiness as she could... until she discovers VideoGames a few minutes into the first episode/cut to sometime later in the manga. Next time we see her, she has turned into the rude, lazy, cynical, and apathetic slob she will be for the rest of the show, even going so far as to refer to herself as a ''FallenAngel''.

* This trope happens subtly to Nate Adams from ''Anime/YokaiWatch'', compared to the video games. Halfway into the series, he becomes less willing to reason with [[MonsterOfTheWeek the Yo-kai from a particular segment]] and more inclined to summon one of his Yo-kai friends to find the way to circunvent their mischievings caused by inspiriting, or outright give them a beating (Jibanyan being his most used choice is an indication), such as his a personal beef with Snottle [[spoiler:without knowing he created him [[note]]as one of his snots when he was younger[[/note]] and he never tries to reason to him]]. Ironically, in the games, fighting Yo-kai is needed to befriend them [[note]]Only a handful of Yo-kai are befriended automatically as the plot progresses, so to build their collection the player must engage Yo-kai in combat, impress them and/or give them their favorite food to earn their friendship (also, some S-rank Yo-kai like Venoct, Kyubi, Arachnus, Toadal Dude and the Super Hero Yo-kai are only available post-game)[[/note]]. The fact that he hates being average [[note]]so much that he allowed a Yo-kai to lick him ''everywhere'' to get prizes[[/note]] and that almost every day of his life is thrown upside-down by Yo-kai themselves has to do with it.